There is no real one stop shop, if there were it would be the only site out there.

There are times they have the best fares, but there are times they don't and you can do much better either dollar wise or schedule wise going to other sites.

I'll start there usually to get a ball park figure, then look other places to see if there are better fares, which there sometimes are.

For rentals I find them totally useless, not that you asked on that one.